The boundary layer type semiconductor ceramic capacitors are characterized by large apparent permittivity as compared with the conventional ceramic capacitors, and therefore, they have been used widely.
It is known that such a semiconductor ceramic capacitors may be produced by a process comprising the steps of: firing, in a neutral or reducing atmosphere, shaped bodies of a ceramic material of a barium titanate or strontium titanate system in which is incorporated at least one valency control element such as a rare earth element, Nb, Sb or Bi, heat-treating the resultant semiconductor ceramic bodies to which an insulatorizing agent such as metal or a compound thereof, for example, copper, bismuth, manganese, lead or their compounds, is applied, and then forming opposite electrodes on surfaces of the heat-treated semiconductor ceramic bodies.
When heat-treating the semiconductor ceramic bodies to insulatorize the crystal grain boundary of the semiconductor ceramics, the semiconductor ceramic bodies are applied with a paste of the insulatorizing agent, placed side by side or one on another in a saggar, and then heated in a furnace. In this process, however, there is a temperature difference in the sagger during heat-treatment or an atmosphere difference in the furnace due to the evaporated metal or its compounds, resulting in large scattering in the characteristics of the produced boundary layer semiconductor ceramic capacitors. Further, firing tends to cause partial welding between the semiconductor ceramic bodies. For these reasons, it is difficult to produce boundary layer semiconductor ceramic capacitors of good quality with high yield.